Copying CDs

[bscott at ntisys.com]

On 26 Apr 2004, at 11:58am, jbd at codemeta.com wrote:
> I seem to remember from a long time ago, that just dd'ing a CD (or hard
> drive for that matter) didn't produce workable results. Looks like things
> have gotten better since then.

  It's one of those "it depends" things.  With CDs, between all the
different standards, and all the variations and violations different vendors
have added, not all CDs will play nice with a simple "dd" command.  The El
Torito spec, though, is, as I understand it, a fairly simple extension to
ISO-9660.  This is evident in that fact that bootable ISO images downloaded
from the 'net don't require any special commands to "cdrecord" when burning.  
With hard disks, again, "it depends".  Some things care about things like
C/H/S geometry and geometry translation, other things don't.  Exactly which
things care, and how, is arcane to the extreme.

  One of the things I still haven't figured out but am rather curious about
is that if I download a Red Hat CD image, use "cdrecord" to burn it, and
then boot and run a "mediacheck", it will pass just fine.  But if I do

	diff -q /dev/cdrom /path/to/cdimage.iso

then I get a mismatch (/dev/cdrom ends prematurely).  I don't get how it can
pass Red Hat's media check but not diff properly.

  Here there be dragons.

-- 
Ben Scott <bscott at ntisys.com>
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